How Many Ounces Are in a Gallon? Your Simple Oz-to-Gallon Conversion Guide

Let’s be real. Understanding how many ounces are in a gallon makes hydration tracking a whole lot easier — especially when you’re trying to choose the right Stanley for your day.

Whether you reach for a classic tumbler, love a leakproof bottle, or can’t leave the house without an insulated mug full of soothing tea, knowing how to convert oz to gallons to cups lets you make smarter hydration choices.

And that’s where we can help.

You don’t have to be a mathlete to work out if you’re giving your body the fluids it needs. We’ve been perfecting the art of hydration since 1913 — and we’re willing to let you in on a secret or two.

Just check out our oz-to-gallon conversion tables below to find out how many ounces are in a gallon, how many ounces are in a cup, and how many times you need to refill your chosen Stanley to reach your recommended daily water intake.

But first, let’s get to the question you came here for: how many ounces in a gallon? The answer is 128. Yep, 1 gallon = 128 fluid ounces.

Oz-to-Gallon Conversion Chart

Okay, so we’ve been over how many ounces are in a gallon. But what about ½ a gallon, a quart, or a cup?

We’ve done all the hard oz-to-gallon conversion work for you to figure that out: 

Wanna stay super hydrated? Our Adventure tumblers and IceFlow™ jugs hold up to ½ a gallon, equivalent to 64 fluid ounces. But it’s our 2.5-quart Vacuum Bottle that takes top spot as the biggest product in our lineup. All are perfect for those long days out.

How Stanley Sizes Translate to “Cups”

When you think of Stanley, you might think of cups — we’re famous for making great travel ones, after all — but we actually always measure our tumblers, water bottles, and mugs in fluid ounces. It’s a personal preference, what can we say?

But if you prefer cups over ounces (we won’t judge!), here’s how our Stanley range measures up.

How Many Stanleys are in a Gallon?

Let’s recap. So we know 1 gallon = 128 ounces. And, with a lil’ research, we know that women should drink around 91 fluid ounces of water every day, and men should drink around 125 fluid ounces.

So, how many times do you need to fill your Stanley to get to a full gallon — or at least the required intake? We’ve created a super convenient table to help you track your daily water intake and figure out which Stanley size to buy to achieve your hydration goals.

From here, all you gotta do is match your Stanley to your needs. Escaping the routine for a day out on the trails? Opt for a larger Stanley to keep you hydrated all day. Staying home while tackling the chore list? When you’re within easy reach of a refill, a smaller Stanley fits easily into your day (and your shopping bag).

Ready to find your perfect fit? Shop all Stanley insulated drinkware.

FAQs About Converting Oz to Gallons

How many ounces are in a gallon of water?

There are 128 fluid ounces in a gallon of water. This is around the recommended daily water intake for men (124 fluid ounces) and a little more than the recommended daily intake for women (91 fluid ounces).

How many ounces are in a half-gallon?

There are 64 fluid ounces in a half-gallon. There are 128 fluid ounces in a full gallon.  

Is a gallon of water always 128 ounces?

Yes, no matter how you pour it, a gallon of water is always equivalent to 128 fluid ounces. You can also represent a gallon of water as 4 quarts, 8 pints, or 16 cups.